1. Field of the Invention
The present invention relates to a method of manufacturing a die, starting with a conducting surface, provided with a pattern of an insulating material, by means of which die a sieve for screen printing can be manufactured in an electrolytic manner.
2. Description of the Prior Art
Dies of said type have been used in the art; they comprise a flat or a curved surface or they may consist of a closed cylinder, the conducting surface being a metal or another material, which is provided with a conducting upper layer.
An electrolytic manufacture of the respective sieve material has also been used in the art and is disclosed in the West German Magazine "METALLOBERFLACHE" 19th issue, volume 12, December 1965, pages 369-372. The respective die comprises a flat or curved sheet and in particular cases, also a cylinder having an electrically conducting surface, mostly consisting of a metal such as aluminium, copper, steel, nickel or chromium, upon which a pattern or grate is applied of insulating parts, which pattern corresponds with the pattern of the desired pores in the screen printing sieve to be manufactured. The insulating parts upon the die surface may be obtained by various different methods, e.g. by means of a photographic method, whereby a layer is applied upon the die surface, which layer is sensitive to electromagnetic radiation, said layer having the desired insulating properties. The layer is subjected to electromagnetic radiation through a mask, comprising a positive or negative image of the desired perforation pattern, which electromagnetic radiation is so carried out that after completion of the same and an eventual development, the concerning die surface comprises the desired pattern of insulating parts.
Said method is unsatisfactory, as said insulating parts will slightly project above the die surface, such, that on manufacturing the sieve material and at the subsequent removal from the die surface, said insulating parts will be damaged in such a manner that only one sieve or at most a very limited number of sieves may be manufactured upon said die surface. It will be obvious that the life of the respective die surface will be very restricted, due to the necessity of using an electromagnetic-radiation-sensitive product for applying said insulating parts.
Another method, which is used in the art and by means of which it is generally possible to obtain considerably more sieve material by means of a die surface, than by means of the first mentioned method, is based upon the conception to so countersink the desired pattern of insulating parts in the die surface, that the top of the points to be insulated is flush with the surface of the die material or is even situated slightly therebelow. Such a die surface is obtained by first providing a metal surface with a pattern of recessed pockets, which are subsequently filled with an insulating material, for instance a plastic resin, whereupon the entire die surface is polished. Said pattern of recessed pockets may either be applied mechanically, for instance by means of impressing or cutting, or chemically by etching, or in a physical manner.
The difficulty with said second method is that it does not render the number of sieves to be manufactured upon such a die, to be unlimited, as the adherence of the employed plastic resins in the recessed pockets, may disadvantageously be impaired as a result of the chemical processes occurring during the respective electrolysis.